7. DHCP Lease & Handshake
DHCP Lease Table – Quick Overview
The Lease Table is the router’s record of which IPs are “rented” and to whom.
| Column | What It Shows | Example |
|---|---|---|
| IP Address | Assigned address | 192.168.1.10 |
| MAC Address | Device hardware ID | A:B:C:D:E:F |
| Hostname | Device name | DESKTOP-PC1 |
| Lease Start/End | When IP was given & expires | 2024-05-20 10:00:00 |
| Lease Type | Dynamic (temporary) or Static | Dynamic |
Key Points:
- Devices rent IPs; they don’t own them.
- The router checks the table to avoid IP conflicts.
- During DORA, IPs go Pending at Offer and Locked at ACK.
DHCP “Secret Handshake” (How Client & Server Recognize Each Other)
| Feature | Purpose |
|---|---|
| Transaction ID (xid) | Random code from client : must match in server’s Offer/ACK. Prevents mix-ups. |
| DHCP Message Type | Labels the packet: Discover (1), Offer (2), Request (3), ACK (5). |
| UDP Ports 67/68 | Only server (67) and client (68) listen ; ignores other traffic. |
| chaddr (MAC) | Ensures server assigns IP to the correct NIC. |